ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-7-4149-2007 3-D polarised simulations of space-borne passive mm/sub-mm midlatitude cirrus observations: a case study Davis C. P. 1 Evans K. F. 2 Buehler S. A. 3 Wu D. L. 4 Pumphrey H. C. 1 Institute of Atmospheric and Environmental Science, University of Edinburgh, Edinburgh, UK Dept. of Atmosphere and Oceanic Sciences, University of Colorado, Boulder, USA Department of Space Science, Lulea Technical University, Kiruna, Sweden Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA 07 08 2007 7 15 4149 4158 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/7/4149/2007/acp-7-4149-2007.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/7/4149/2007/acp-7-4149-2007.pdf

Global observations of ice clouds are needed to improve our understanding of their impact on earth's radiation balance and the water-cycle. Passive mm/sub-mm has some advantages compared to other space-borne cloud-ice remote sensing techniques. The physics of scattering makes forward radiative transfer modelling for such instruments challenging. This paper demonstrates the ability of a recently developed RT code, ARTS-MC, to accurately simulate observations of this type for a variety of viewing geometries corresponding to operational (AMSU-B, EOS-MLS) and proposed (CIWSIR) instruments. ARTS-MC employs an adjoint Monte-Carlo method, makes proper account of polarisation, and uses 3-D spherical geometry. The actual field of view characteristics for each instrument are also accounted for. A 3-D midlatitude cirrus scenario is used, which is derived from Chilbolton cloud radar data and a stochastic method for generating 3-D ice water content fields. These demonstration simulations clearly demonstrate the beamfilling effect, significant polarisation effects for non-spherical particles, and also a beamfilling effect with regard to polarisation.

 References Atkinson, N. C.: Calibration, monitoring and validation of AMSU-B, Adv. Space Res., 28(1), 117–126, 2001. Buehler, S. A.: Cloud Ice Water Submillimeter Imaging Radiometer (CIWSIR) Mission Proposal, http://www.sat.uni-bremen.de/projects/ciwsir/cirrus_expl_2005_09_05.pdf, 2005. Davis, C., Emde, C., and Harwood, R.: A 3D Polarized Reversed Monte Carlo Radiative Transfer Model for mm and sub-mm Passive Remote Sensing in Cloudy Atmospheres, IEEE Trans. Geosci. Remote Sensing, 43, 1096–1101, 2005a. Davis, C P., Wu, D L., Emde, C., Jiang, J H., Cofield, R E., and Harwood, R S.: Cirrus Induced Polarization in 122 GHz Aura Microwave Limb Sounder Radiances, Geophys. Res. Lett, 32, L14806, doi:10.1029/2005GL022681, 2005b. Evans, K. F., Walter, S. J., Heymsfield, A. J., and McFarquhar, G. M.: Submillimeter-Wave Cloud Ice Radiometer: Simulations of retrieval algorithm performance, J. Geophys. Res., 107(D3), 4028, doi:10.1029/2001JD000709, 2002. Giraud, V., Buriez, J. C., Fouquart, Y., Parol, F., and Seze, G.: Large-scale analysis of cirrus clouds from AVHRR data: Assessment of both a microphysical index and the cloud-top temperature, J. Appl. Met., 36, 664–675, 1997. Hogan, R J. and Kew, S F.: A 3D stochastic cloud model for investigating the radiative properties of inhomogeneous cirrus clouds, Q. J. R. Meteorol. Soc., 131, 2585–2608, 2005. Houghton, J., Ding, Y., Griggs, D., Noguer, M., van~der Linden, P., Dai, X., Maskell, K., and Johnson, C. A. (Eds.): IPCC, 2001: Climate Change 2001: The Scientific Basis, Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, 2001. Kummerow, C.: Beamfilling Errors in Passive Microwave Rainfall Retrievals, J. Appl. Meteorol., 37, 356–370, 1998. Lafont, D. and Guillimet, B.: Subpixel fractional cloud cover and inhomogenety effects in microwave beam filling error, Atmos. Res., 72, 149–168, 2004. Lynch, D., Sassen, K., Starr, D O., and Stephens, G.: Cirrus, Oxford University Press, 2002. McCollum, J. and Krajewski, W.: Investigations of error sources of the Global Precipitation Climatology Project emission algorithm, J. Geophys. Res., 103, 28 711–28 719, 1998. McFarquhar, G. and Heymsfield, A.: Parametrization of tropical ice crystal size distributions and implications for radiative transfer: Results from CEPEX, J. Atmos. Sci., 54, 2187–2200, 1997. Minnis, P., Heck, P. W., and Young, D. F.: Inference of cirrus cloud properties using satellite-observed visible and infrared radiances. Part II: Verification of theoretical cirrus radiative properties, J. Atmos. Sci., 50, 1305–1322, 1993. Mishchenko, M.: Calculation of the amplitude matrix for a nonspherical particle in a fixed orientation, Appl. Opt., 39, 1026–1031, 2000. Mishchenko, M. I., Rossow, W. B., Macke, A., and Lacis, A. A.: Sensitivity of cirrus cloud albedo, bidirectional reflectance and optical thickness retrieval accuracy to ice particle shape, J. Geophys. Res., 101(D12), 16 973–16 986, doi:10.1029/96JD01155, 1996. Mishchenko, M. and Travis, L.: Capabilities and limitations of a current FORTRAN implementation of the T-matrix method for randomly oriented, rotationally symmetric scatterers, J. Quant. Spectrosc. Radiat. Transfer, 60, 309–324, 1998. Ou, S. C., Liou, K. N., Takano, Y., Rao, N. X., Fu, Q., Heymsfield, A. J., Miloshevich, L. M., Baum, B., and Kinne, S. A.: Remote sounding of cirrus cloud optical depths and ice crystal sizes from AVHRR data: Verification using FIRE II IFO measurements, J. Atmos. Sci., 52, 4143–4158, 1995. Platnick, S., Li, J. Y., King, M. D., Gerber, H., and Hobbs, P. V.: A solar reflectance method for retrieving the optical thickness and droplet size of liquid water clouds over snow and ice surfaces, J. Geophys. Res., 106(D14), 15 185–15 199, 2001. Rolland, P., Liou, K. N., King, M. D., Tsay, S. C., and McFarquhar, G. M.: Remote sensing of optical and microphysical properties of cirrus clouds using Moderate-Resolution Imaging Spectroradiometer channels: Methodology and sensitivity to physical assumptions, J. Geophys. Res., 105, 11 721–11 738, 2000. Rossow, W. B. and Schiffer, R. A.: Advances in understanding clouds from ISSCP, Bull. Amer. Meteor. Soc., 80, 2261–2287, 1999. Stephens, G. L., Vane, D. G., Boain, R. J., Mace, G. G., Sassen, K., Wang, Z., Illingworth, A. J., O'Connor, E. J., Rossow, W. B., Durden, S. L., Miller, S. D., Austin, R. T., Benedetti, A., Mitrescu, C., and CloudSat Science Team: The CloudSat mission and the A-train: A new dimension of space-based observations of clouds and precipitation, Bull. Amer. Meteor. Soc., 83, 1771–1790, doi:10.1175/BAMS-83-12-1771, 2002. Stubenrauch, C., Holz, R., Chedin, A., Mitchell, D. L., and Baran, A. J.: Retrieval of cirrus ice crystal sizes from 8.3 and 11.1 micron emissivities determined by the improved initialization inversion of TIROS-N Opertional Vertical Sounder observations, J. Geophys. Res., 104, 793–808, 1999. Waters, J. W., Froidevaux, L., Harwood, R. S., et al.: The Earth Observing System Microwave Limb Sounder (EOS MLS) on the Aura satellite, IEEE Trans. Geosci. Remote Sensing, 44(5), 1075–1092, 2006. Wilheit, T., Chang, A., Rao, M., Rodgers, E., and Theon, J.: A satellite technique for quantitatively mapping rainfall rates oer the oceans, J. Appl. Meteorol., 16, 551–560, 1977.